Replacing carpet in hall and stairway

I need to replace the carpet in a hallway and on some stairs. The stairs have a right-angle turn at the bottom. With the hallway, it's a very irrregular shape due to doorways and closets. Preferably this would be a single carpet for both.

I was wondering how this is done and how much it would cost. I'd imagine I could install carpet myself in a rectangular room, but it seems like it might be pretty complicated getting this carpet to fit. I don't know if every little detail would be measured and planned, or just laid down and cut until it fits. I was thinking it might be best to hire somebody. I'm pretty sure we can afford to buy the carpet itself, but I have no idea how much this should cost for installation. That's why I'm writing here, hoping I could get some input on that.

I can't give you a dollar figure, but carpet layers are not extremely expensive, and I think you'd be wise to hire it out. Laying carpet seems easy enough, but it has to be stretched to fit properly, and your stairway sure isn't where you'd want a wrinkle to stub a toe on. If you haven't already got the carpet, the dealer can set you up with an installer.

My stairs are layed out in a similar manner...the carpet was installed in numerous pieces. basically, they went from just under the top of the upper tread, down the riser, over the tread and over the lip. You'd never get a single piece to fit and stay in place with all of those angles.